1. Field of the Invention
The present invention relates to a processing method for an optical device composed of a sapphire substrate and an epitaxial film formed on the sapphire substrate.
2. Description of the Related Art
A nitride semiconductor such as gallium nitride (GaN) has a wide bandgap and allows the emission of blue light, so that it is widely used for the manufacture of LED (Light Emitting Diode) and LD (Laser Diode). A general gallium nitride based light emitting diode has a structure composed of a sapphire substrate, a buffer layer of a gallium nitride based compound such as AlGaN formed on the sapphire substrate, an n-GaN layer formed on the buffer layer, a light emitting layer (MQW: Multiple Quantum Well structure) of a GaN/InGaN layer formed on the n-GaN layer, and a p-GaN layer formed on the light emitting layer (see Japanese Patent No. 3250438, for example).
Such an epitaxial film of gallium nitride is formed on the front side of the sapphire substrate, and the back side of the sapphire substrate (opposite to the epitaxial film) is next ground by using a grinding apparatus as disclosed in Japanese Patent Laid-open No. 2011-044471, for example, thereby reducing the thickness of the sapphire substrate to a predetermined thickness. Thereafter, the sapphire substrate is divided into individual optical devices by using a laser processing apparatus or a cutting apparatus.